The present invention generally applies to wireless communication networks, and particularly applies to improving call routing efficiencies where an inter-MSC handoff is involved.
Wireless communication networks based on TIA/EIA/IS-2000 standards (cdma2000 networks) interface with public data networks (PDNs), such as the Internet, as well as with traditional circuit-switched networks, such as the Public Switched Telephone Network (PSTN). These networks typically include complementary sets of network entities, some shared, to support both data (packet-switched) and voice (circuit-switched) calls. For example, mobile switching centers (MSCs) within the wireless communication network provide call management (setup/teardown, etc.) services, as well as providing a communications link from the wireless network to the PSTN. Thus, MSCs play a central role in managing voice traffic between the wireless network and the PSTN.
In data calls, while the MSC is still involved in certain aspects of call setup/teardown, it does not carry the packet data traffic. Rather a packet control function (PCF) communicatively links the radio network to a packet data serving node (PDSN), which is coupled to the PDN. These routing differences between voice and data calls affect the manner in which wireless communication networks, and the various entities within those networks, manage call routing. In some instances, the routing differences lead to certain inefficiencies.
For example, routing inefficiencies can arise as a wireless network user moves from one location to another. The wireless communication network(s) must track movement of the user as the user moves through different coverage areas. The user may move between coverage areas comprising a single wireless communication network, or may cross the coverage area of multiple wireless communication networks. In either case, standard signaling protocols exist for passing cellular subscriber information from one carrier to another. One such protocol is TIA/EIA/ANSI-41, commonly referred to as IS-41. IS-41 is a standard for inter-switch signaling and permits users to roam across the wireless networks of many different carriers (network operators) by allowing the various network entities to track the location of the user via standardized protocol messages. Commonly, IS-41 messages are carried via System Signaling 7 (SS7) networks
IS-41 standards provide standardized methods for mobile station registration, authentication, and handoff. For example, IS-41 allows a remote network to inform a home network that a user has registered for service through the remote network. If a call is placed to the user, a home location register (HLR) in the home network provides this information to assist in call routing. How that call is routed and what network elements are involved depends on the type of call, and it is in that distinction that at least one area of potential call routing inefficiency arises.
For example, with circuit-switched calls (e.g., mobile terminated or originated voice calls), a particular MSC provides the circuit-switched link to the PSTN. That MSC is referred to as the “anchor” MSC. As the mobile moves from the coverage area of the anchor MSC, it is handed off to another MSC, which is referred to as the “serving” MSC. Because the PSTN connection remains with the anchor MSC, voice traffic for the call is routed through the anchor MSC and the serving MSC. A bearer service for this traffic is established on inter-MSC trunk lines. Once the call ends, the mobile may originate another call or re-register with the network, thereby establishing a new anchor MSC.
For data packet calls, the MSCs are not required to establish bearer services for the packet data traffic because that type of call traffic is routed through other network entities such as packet control functions (PCFs) and packet data serving nodes (PDSNs). Nonetheless, inter-MSC handoffs follow signaling conventions similar to those used for circuit-switched call handoffs, and the notion of anchor and serving MSC still applies, even though the MSCs are not needed for bearer service in this context. Note that IS-41 has extensions defined by PN-4720 (PN4720 TIA/EIA-41-D Network Based Enhancements for CDMA Packet Data Service) for packet data call-related signaling.
Once consequence of the above approach to packet data call handoff is that circuit-switched call routing inefficiency may be unnecessarily incurred for mobile stations that have undergone an inter-MSC handoff while engaged in an active packet data call. For example, a mobile station engaged only in a packet data call moves from the coverage area of its anchor MSC to a new MSC, which becomes the serving MSC. Any circuit switched call incoming to the mobile is routed through the anchor MSC to the serving MSC, when, ideally, it should have been routed directly to the serving MSC.
This undesirable routing of voice call traffic is inheren/unavoidable with the existing standards, because the anchor MSC does not change until a subsequent call origination or registration event performed by the MS after termination of the current call. Thus, CDMA wireless communication networks need a more efficient approach to IS-41/PN-4720 based call routing. Preferably, this solution would be standards-compliant and unobtrusive to users.